On-board battery consumption, cellular disconnectivity, and frequent handoff are key challenges for unmanned aerial vehicle (UAV) based delivery missions, a.k.a., cargo-UAV. Indeed, with the introduction of UAV technology into cargo shipping and logistics, designing energy-efficient paths becomes a serious issue for the next retail industry transformation. Typically, the latter has to guarantee uninterrupted or slightly interrupted cellular connectivity for the UAV’s command and control through a small number of handoffs. In this paper, we formulate the trajectory planning as a multi-objective problem aiming to minimize both the UAV’s energy consumption and the handoff rate, constrained by the UAV battery size and disconnectivity rate. Due to the problem’s complexity, we propose a dynamic programming based solution. Through simulations, we demonstrate the efficiency of our approach in providing opti-mized UAV trajectories. Also, the impact of several parameters, such as the cargo-UAV altitude, disconnectivity rate, and type of environment, are investigated. The obtained results allow to draw recommendations and guidelines for cargo-UAV operations.

In this paper, we analyze the downlink coverage probability and rate of an aerial user in vertical HetNets (VHetNets) comprising aerial base stations (aerial-BSs) and terrestrial-BSs. The locations of terrestrial-BSs are modeled as an infinite 2-D Poisson Point Process (PPP), while the locations of aerial-BSs are modeled as a finite 2-D Binomial Point Process (BPP). Our cellular-to-air (C2A) channel model incorporates line-of-sight (LoS) and non-LoS transmissions between terrestrial-BSs and a typical aerial user, while we assume LoS transmissions for all aerial links. We assume that the aerial user is associated with an aerial-BS or terrestrial-BS that provides the strongest average received power. Using stochastic geometry, we derive exact and approximate expressions of the coverage probability and rate in terms of interference power's Laplace transform. The expressions are simplified assuming only LoS transmissions for the C2A channels. This enables easy-to-compute equations with good accuracy at elevated aerial user heights. We find that aerial users hovering at low altitudes tend to connect to aerial-BSs in denser terrestrial environments. Employing directive beamforming at aerial-BSs guarantees an acceptable performance at the aerial user by reducing interference signals received from the aerial-BSs. In denser terrestrial networks, the performance at the aerial user degrades substantially despite beamforming.

Unmanned aerial vehicles (UAVs) can be users that support new applications, or be communication access points that serve terrestrial and/or aerial users. In this paper, we focus on the connectivity problem of aerial users when they are exclusively served by aerial base stations (BS), i.e., UAV-BSs. Specifically, the 3D placement problem of a directional-antenna equipped UAV-BS, aiming to maximize the number of covered aerial users under a spectrum sharing policy with terrestrial networks, is investigated. Given a known spectrum sharing policy between the aerial and terrestrial networks, we propose a 3D placement algorithm that achieves optimality. Simulation results show the performance of our approach, in terms of number of covered aerial users for different configurations and parameters, such as the spectrum sharing policy, antenna beamwidth, transmit power, and aerial users density. These results represent novel guidelines for exclusive aerial networks deployment and applications, distinctively for orthogonal and non-orthogonal spectrum sharing policies with terrestrial networks.

Use of aerial base stations (ABSs) is a promising approach to enhance the agility and flexibility of future wireless networks. ABSs can improve the coverage and/or capacity of a network by moving supply towards demand. Deploying ABSs in a network presents several challenges such as finding an efficient 3D-placement of ABSs that takes network objectives into account. Another challenge is the limited wireless backhaul capacity of ABSs and consequently, potentially higher latency incurred. Content caching is proposed to alleviate the backhaul congestion and decrease the latency. We consider a limited backhaul capacity for ABSs due to varying position-dependent path loss values and define two groups of users (delay-tolerant and delay-sensitive) with different data rate requirements. We study the problem of jointly determining backhaul-aware 3D placement for ABSs, user-BS associations and corresponding bandwidth allocations while minimizing total downlink transmit power. Proposed iterative algorithm applies a decomposition method. First, the 3D locations of ABSs are found using semi-definite relaxation and coordinate descent methods, and then user-BS associations and bandwidth allocations are optimized. The simulation results demonstrate the effectiveness of the proposed algorithm and provide insights about the impact of traffic distribution and content caching on transmit power and backhaul usage of ABSs.

In this paper, we propose a framework design for wireless sensor networks based on multiple unmanned aerial vehicles (UAVs). Specifically, we aim to minimize deployment and operational costs, with respect to budget and power constraints. To this end, we first optimize the number and locations of cluster heads (CHs) guaranteeing data collection from all sensors. Then, to minimize the data collection flight time, we optimize the number and trajectories of UAVs. Accordingly, we distinguish two trajectory approaches: 1) where a UAV hovers exactly above the visited CH; and 2) where a UAV hovers within a range of the CH. The results of this include guidelines for data collection design. The characteristics of sensor nodes' K-means clustering are then discussed. Next, we illustrate the performance of optimal and heuristic solutions for trajectory planning. The genetic algorithm is shown to be near- optimal with only 3:5% degradation. The impacts of the trajectory approach, environment, and UAVs' altitude are investigated. Finally, fairness of UAVs trajectories is discussed.

Ubiquitous wireless connectivity is critical for the operation of aerial users. In this paper, we investigate the downlink coverage probability of a typical aerial user served by a network of terrestrial-BSs and aerial-BSs, which we refer to as the vertical HetNet (VHetNet). We model the terrestrial- BSs as an infinite 2-D Poisson point process (PPP) and aerial-BSs as a finite 2-D Binomial point process (BPP). A typical aerial user is assumed to be associated with the BS that provides the strongest biased average received signal power. Closed-form expressions for the association probabilities to a terrestrial-BS and an aerial-BS are derived. Under the assumption of an interference-limited network, we derive an expression for the coverage probability in terms of the Laplace transform of the aggregate interference power. Several design insights are presented, showing that the coverage probability does not have a steady behavior with the aerial user height; and a denser aerial-BS network improves the overall coverage probability. Moreover, the results reveal that the coverage probability under unbiased aerial user association always outperforms its biased counterpart.

This paper considers an aerial base station (aerial-BS) assisted terrestrial network where user mobility is taken into account. User movement changes the network dynamically which may result in performance loss. To avoid this loss, guarantee a minimum quality-of-service (QoS) and possibly increase the QoS, we add an aerial-BS to the network. For fair comparison between the conventional terrestrial network and the aerial-BS assisted one, we keep the total number of BSs identical in both networks. Obtaining the best performance in such networks highly depends on the optimal placement of the aerial-BS. To this end, an algorithm which can rely on general and realistic assumptions and can decide where to go based on the past experiences is required. The proposed approach for this goal is based on a discounted reward reinforcement learning which is known as Q-learning. Simulation results show this method provides an effective placement strategy which increases the QoS of wireless networks when it is needed and promises to find the optimum position of the aerial-BS in discrete environments.

Heterogenous networks (HetNets) using different size cells and several different networks with multiple wireless access technologies can provide large capacities while also improving the localization accuracy. In this paper, we propose a novel received signal strength (RSS) based inter-network cooperative localization framework based on a Metropolis-Hastings (MH) algorithm for two-tier HetNets with unknown transmit powers. Through the MH based estimation methodology, the unknown position of user equipment and transmit powers of base stations (BSs) are jointly estimated. The validity of the proposed method is confirmed by simulation results.

Drone base stations (DBSs) can enhance network coverage and area capacity by moving supply towards demand when required. This degree of freedom could be especially useful for future applications with extreme demands, such as ultra reliable and low latency communications (uRLLC). However, deployment of DBSs can face several challenges. One issue is finding the 3D placement of such BSs to satisfy dynamic requirements of the system. Second, the availability of reliable wireless backhaul links and the related resource allocation are principal issues that should be considered. Finally, association of the users with BSs becomes an involved problem due to mobility of DBSs. In this paper, we consider a macro-BS (MBS) and several DBSs that rely on the wireless links to the MBS for backhauling. Considering regular and uRLLC users, we propose an algorithm to find efficient 3D locations of DBSs in addition to the user-BS associations and wireless backhaul bandwidth allocations to maximize the sum logarithmic rate of the users. To this end, a decomposition method is employed to first find the user-BS association and bandwidth allocations. Then DBS locations are updated using a heuristic particle swarm optimization algorithm. Simulation results show the effectiveness of the proposed method and provide useful insights on the effects of traffic distributions and antenna beamwidth.

Computer displays emit electromagnetic waves, which compromise the information displayed by the computer. This can be a potential information security threat as the sensitive information can be stolen from a distance without leaving any trace. The video leakage signals contain the information of the image displayed in the computer, so the video leakage signals can be seen as special image signals. However, different from the normal image signal, the signal to noise ratio (SNR) of video leakage signal is low due to the environmental noise and many other man-made noises. In this paper, a novel wavelet based independent component analysis (ICA) method is proposed for improving SNR of computer video leakage signals. By using this method, we can improve the performance of pre-processing of computer video leaking signals. We solve the problem of using Fast ICA in processing video leakage signal by using a wavelet filter. The performance of Fast ICA is improved by working in wavelet domain because of advantages like ease of implementation and less computation time when compared to time domain. We pre-process one-dimensional received signal without reconstructing the image since it is inefficient to reconstruct signal before processing. A direct SNR can't be defined. Therefore, another metric called quasi signal to noise ratio (QSNR) is defined to estimate signal to noise ratio of video leakage signals. The processed results of the actual experimental data show that the proposed wavelet based ICA algorithm has a better performance than the Fast ICA algorithm and the Wavelet denoising algorithm.

Using drone base stations (drone-BSs) in wireless networks has started attracting attention. Drone-BSs can assist the ground BSs in both capacity and coverage enhancement. One of the important problems about integrating drone-BSs to cellular networks is the management of their placement to satisfy the dynamic system requirements. In this paper, we propose a method to find the positions of drone-BSs in an area with different user densities using a heuristic algorithm. The goal is to find the minimum number of drone-BSs and their 3D placement so that all the users are served. Our simulation results show that the proposed approach can satisfy the quality-of-service requirements of the network.

In this paper, performance of two-way full-duplex cooperative systems under residual loop- interference (LI) is analyzed in terms of outage probability over Nakagami-$m$ fading channels. At the relay node of the proposed system, physical- layer-network-coding technique and variable-gain full-duplex amplify-and-forward relaying method are combined for two-way transmission. End-to-end signal-to-interference-plus-noise-ratio (SINR) expression is derived for different power transmissions at the source and relay nodes. New exact outage probability expression is obtained in a single-integral form by using cumulative distribution function of the end-to-end SINR. The analytical results are verified by Monte-Carlo simulations. We also provide lower-bound and asymptotic expressions in closed-form for the outage performance. It is shown that the outage performance of the system is enhanced as long as either the transmit power or the efficiency of LI cancellation process increases. We also observe that the outage probability converges to an error floor due to the residual LI component at the source and relay nodes.

In received signal strength (RSS) based localization problems, the accuracy of the position information obtained is closely associated with the RSS model used. Therefore, positioning success can be improved with a more accurate RSS model. In this study, to analyze the effect of RSS model in localization performance, lognormal mixture shadowing model is used that provides a more accurate RSS model than the classical lognormal shadowing model. For the corresponding mixture model, a tight upper bound for Cramer-Rao lower bound (CRLB) based on Jensen's inequality is derived. The obtained expressions are used in CRLB analyses that are employed in determination of the best estimates in localization. The improved localization accuracy with lognormal mixture shadowing model is demonstrated by means of examining various numerical analyses.

We propose a simple, yet accurate, interference prediction model using the widely used two-ring hexagonal network layout in the absence or presence of shadowing. The proposed model only considers two dominant interferers out of the 18 ones that surround the serving base station. The proposed model, in contrast to the fluid model, takes the radial direction into account. This makes our proposed model more accurate than the fluid model as is validated by computer simulations. Using the proposed model, the conditional probability of outage in the presence of shadowing is derived and its accuracy is shown to be within a fraction of a dB for most scenarios and no worse than 2 dB for few exceptional ones. The analysis presented in this paper gives useful insight with respect to the role played by interference in cellular networks.

Interference cartographs can be utilized to determine no-transmit zones and to set the interference-free transmit power for secondary users in cognitive radio networks. This paper provides a performance comparison of common interpolation techniques for generating interference cartographs. The performances of natural-neighbor, thin-plate spline and kriging interpolations are evaluated in terms of primary emitter localization accuracy and RF field strength estimation efficiency. The simulation results suggest that the natural-neighbor interpolation technique achieves the same level of accuracy and provides more desirable features suitable for cognitive radio networks.

The aggregate interference distribution in cognitive radio networks is studied in a rigorous analytical way using the popular Poisson point process model. While a number of results are available for this model of regular (non-cognitive) networks, cognitive ones present an extra level of difficulty for the analysis, mainly due to the exclusion region around the primary receiver, which are typically addressed via various ad-hoc approximations (e.g. based on the interference cumulants) or via the large-deviation analysis. Unlike the previous studies, here we do not use ad-hoc approximations but rather obtain the asymptotic interference distribution in a systematic and rigorous way. This is in contrast to the large deviation analysis, which provides only the (exponential) order of scaling but not the outage probability itself. Unlike the cumulant-based analysis, our approach provides a guaranteed level of accuracy at the distribution tail. Additionally, our analysis also provides a number of novel insights. In particular, we demonstrate that there is a critical transition point below which the outage probability decays only polynomially but above which it decays exponentially. This provides a solid analytical foundation to the earlier empirical observations in the literature and also reveals how typical outage events occur in different regimes. In addition, the proposed asymptotic expressions are also shown to be accurate in the non-asymptotic regimes.

The aggregate interference distribution in cognitive radio networks is studied in a rigorous analytical way using the popular Poisson point process model. While a number of results are available for this model of regular (non-cognitive) networks, cognitive ones present an extra level of difficulties for the analysis, mainly due to the exclusion region around the primary receiver, which are typically addressed via various ad-hoc approximations (e.g. based on the interference cumulants) or via the large-deviation analysis. Unlike the previous studies, we do not use here ad-hoc approximations but rather obtain the asymptotic interference distribution in a systematic and rigorous way, which also has a guaranteed level of accuracy at the distribution tail. This is in contrast to the large deviation analysis, which provides only the (exponential) order of scaling but not the outage probability itself. Unlike the cumulant-based analysis, our approach provides a guaranteed level of accuracy at the distribution tail. Additionally, our analysis provides a number of novel insights. In particular, we demonstrate that there is a critical transition point below which the outage probability decays only polynomially but above which it decays super-exponentially. This provides a solid analytical foundation to the earlier empirical observations in the literature and also reveals what are the typical ways outage events occur in different regimes. The analysis is further extended to include interference cancelation and fading (from a broad class of distributions). The outage probability is shown to scale down exponentially in the number of canceled nearest interferers in the below-critical region and does not change significantly in the above-critical one. The proposed asymptotic expressions are shown to be accurate in the non-asymptotic regimes.

We present outage capacity analysis and results for the hybrid MIMO scheme we first proposed in. We recently analyzed and demonstrated the FER effectiveness of the proposed algorithm. We also showed that its parallel architecture allows for the tradeoff between complexity, performance and power consumption on a packet-by-packet basis. In this paper we show that despite the fact the Alamouti code (a core component of the proposed algorithm) is capacity-lossy, the overall capacity offered by the proposed scheme is comparable to the one offered by spatial multiplexing algorithms such as MMSE-VBLAST.

In this paper, a methodology for densely packing subcarriers for multicarrier systems is considered. A unit density Weyl-Heisenberg frame is proposed to achieve pulse shaping in multi-carrier communication systems. Hermite pulses are utilized as mother functions to be orthonormalized in pulse shape generation process. The proposed orthonormalized pulse shape, termed as UDALOP, is the first localized pulse shape for unit density multi-carrier communication systems. By using this pulse shape, the need for offset phase value of the O-QAM systems can be eliminated, without losing robustness to frequency dispersion.

In this paper on MIMO-CDMA systems employing permutation spreading, we propose a new method for designing the spreading permutations based on space time block code matrices. We investigate the bit error rate performance of these systems using BPSK and QPSK modulation in single and multiple user situations. The new designs provide full transmit diversity between different message cosets. Compared with spreading permutation designs based on T-designs, the STBC-based spreading permutation designs improve the bit error rate performance without any increase in system complexity.

This paper analyzes the outage probability in cognitive radio networks, based on the Poisson point process model of node spatial distribution and the standard propagation path loss model, including Rayleigh and log-normal fading. To make the analysis tractable, all possible scenarios are classified into three cases based on typical outage events. When the average number of nodes in the forbidden region is much smaller than unity, the aggregate interference can be well approximated by the nearest node for both non-fading and fading scenarios (the nearest node dominates the outage performance). When the average number of nodes in the forbidden region is greater than unity, the aggregate interference can be well approximated by a Gaussian random variable for non-fading scenario (many nodes contribute to outage events, rather than a single dominant one). This approximation also applies to the fading scenario, but its accuracy is a bit worse at the transition region. An alternative approximation is proposed, which is accurate for any outage probability. When the average number of nodes in the forbidden region is slightly smaller than unity, neither the nearest node approximation nor the Gaussian one is accurate for the non-fading scenario (since only a few near-by nodes are dominant), and finding an accurate approximation for the outage probability in this case is an open problem. The alternative approximation above is accurate for the fading scenario. All approximations are validated via Monte-Carlo simulations.

We study analog decoders in an abstract level and show that their dynamic equations can change with message representation domain. This result, which is in contrast with the behavior of conventional discrete-time iterative decoders, is derived based on continuity requirement for messages that are passed between processing nodes in analog decoders. In this letter, this requirement is met by assigning low-pass filters between processing nodes that remain unchanged for different message representation domains.

In this paper, we show an ideal analog min-sum decoder, in the log-likelihood ratio domain, can be considered as a piecewise linear system. Many theoretical aspects of these decoders, thus, can be studied analytically. It is also shown that the dynamic equations can become singular for codes with cycles. When it is non-singular, the corresponding dynamic equations can be solved analytically to derive outputs of the decoder. We study the relationship between singularity and error floor and prove that absorption sets with degree two check nodes are singular graphs and under specific conditions the dynamic equations of an analog min-sum decoder can be reduced to that of an absorption set. The proposed approach paves the way for further analytical analysis on the dynamics of analog min-sum decoders and error floor in low-density parity-check codes.

A methodology for doubling the throughput of multi-carrier systems is proposed. Throughput enhancement method is introduced by using pulse shaping in multi-carrier systems. By employing more than one Weyl-Heisenberg frames that are orthonormal both within the frame and in between the frames, the throughput of multi-carrier systems is increased. Different lattice density scenarios are investigated for throughput enhancement. It is shown that by employing the proposed methodology, throughput of a multi-carrier system can be doubled. Theoretical analysis quantifying throughput enhancements are presented and results are supported by simulation studies. A system level comparison is presented for IEEE 802.16 standards. The effects of various impairments are investigated.

Abstract Most wireless local area network performance estimations are done with the assumption of uniformly distributed (UD) users. In practice, however, stations (STAs) are distributed unevenly among access points (APs) in an extended service area, causing congested hot‐spots (HS) and under‐utilized APs. Considering a typical network is made up of multiple APs, having some nodes carrying excessive loads degrades the overall network performance. The system performance can be improved by associating STAs efficiently throughout the network, in a sense sharing the network resources fairly among APs and thus relieving congestion. The association algorithm currently employed in IEEE 802.11 systems, that is specifically designed for residential and small office environments, takes into account signal strength as the only parameter and associates STAs to the closest (in signal strength sense) AP, ignoring its load. Novel user association algorithms are required to solve the problems commonly seen in corporate network environments spanning multiple APs, namely congestion relief and resource sharing. In this work, a distributed and online association algorithm is proposed that demonstrates improved average throughput performance, a balanced load distribution as well as fairness across the network compared to the conventional algorithm. Copyright © 2008 John Wiley & Sons, Ltd.

We consider network coding rates for directed and undirected k-pairs networks. For directed networks, meagerness is known to be an upper bound on network coding rates. We show that network coding rate can be ominus(|V|) multiplicative factor smaller than meagerness. For the undirected case, we show some progress in the direction of the k-pairs conjecture.

Analytic performance of IEEE 802.11 distributed coordination function that takes into account hidden node problem and unsaturated traffic condition is presented for symmetric networks. This enables us to estimate the performance of practical wireless local area networks more accurately. It is shown that the presence of hidden nodes barely affects the network performance in low traffic conditions, but it causes up to 50% performance loss in moderate-to-high traffic scenarios. It is also found that the footprint of the first hidden node had the most decremental effect compared to subsequent hidden nodes. Analytical results presented in the paper are backed by simulation results.

"Eligible for the student paper award." In this work we improve on the bounds presented in Z. Li and B. Li (2004) for network coding gain in the undirected case. A tightened bound for the undirected multicast problem with three terminals is derived. An interesting result shows that with fractional routing, routing throughput can achieve at least 75 % of the coding throughput. A tighter bound for the general multicast problem with any number of terminals shows that coding gain is strictly less than 2. Our derived bound depends on the number of terminals in the multicast network and approaches 2 for arbitrarily large number of terminals.

In this paper, we show that an ideal analog min-sum decoder, in the log-likelihood ratio domain, can be considered as a piecewise linear system. Many theoretical aspects of these decoders, thus, can be studied analytically. It is also shown that the dynamic equations can become singular and degrade the decoding performance. When the decoder is nonsingular, the corresponding dynamic equations can be solved analytically to derive outputs of the decoder. The proposed approach paves the way for further analytical analysis on the dynamics of analog min-sum decoders.

In this paper, we introduce the generalized decorrelating discrete-time RAKE receiver (GD-DTR) for single antenna systems and extend it to multi-antenna (e.g. MIMO) systems. The GD-DTR benefits from the correlated nature of multiple access interference while being robust against channel estimation errors. It is a combination of two other advanced RAKE reception methods namely, the discrete-time version of the generalized RAKE (G-RAKE) receiver and the decorrelating discrete-time RAKE receiver (D-DTR). The G-RAKE was proposed for correlated interference mitigation. The D-DTR improves performance in the presence of channel estimation errors in diffuse channels. Our results show that the performance of the discrete-time G-RAKE (G-DTR) could be worse than a conventional discrete-time RAKE receiver (C-DTR) when there are channel estimation errors in the system. Unlike G-DTR, our proposed GD-DTR provides gains up to 0.7 dB at a raw bit error rate of 10-2in the presence of channel estimation errors compared to C-DTR. For the MIMO case, the gain of the MIMO GD-DTR compared to MIMO C-DTR are 1 dB and 1.1 dB at a raw bit error rate of 10-2in 2 transmit 2 receive antenna (2times2) and 3times3 systems respectively, if there is no correlation between the antennas. For a highly correlated receive antenna case, the gain increases to 4 dB.

In this paper, we propose a novel system architecture for channel estimation and multi-user detection in CDMA systems. Estimation and detection are performed jointly by sequential basis selection algorithms; namely the basic matching pursuit (BMP) algorithm and the orthogonal matching pursuit (OMP) algorithm. We start by demonstrating that the iterations of the BMP algorithm are equivalent to that of the well known detection method, successive interference cancelation (SIC) in code domain. We then introduce the OMP algorithm as a multi-user detector. This novel detection structure orthogonalizes the SIC process hence improves the detection performance. By using simulation results, we demonstrate that its performance is equivalent to decorrelating detector. Inspired from these results, we propose a joint blind channel estimation and detection scheme employing OMP. This novel scheme is less complex than subspace based techniques and gives better performance.

Many wireless local area network (WLAN) performance estimations are done with the assumption of uniformly distributed stations (STAs). In practice, on the contrary STAs are distributed unevenly among access points (APs), causing hot-spots and under utilized APs in a wireless network. Considering a WLAN is made up of multiple APs, having some APs carrying excessive loads (i.e. hot-spots) degrades both the considered APs as well as the overall network performance. The system performance can be improved by associating incoming STAs effectively throughout the network, in a sense to balance the network load evenly between APs and relieve the hot-spot congestion. Currently employed user association method in IEEE 802.11 WLANs considers only the received signal strength of APs at STAs, and associates STAs to the closest (in signal strength sense) AP, ignoring its load and interference value.Novel user association algorithms are required for congestion relief and network performance improvement. In this work, a new distributed association algorithm taking into consideration not only the received signal strength of the APs at STAs but also AP loadings and interference is proposed. A new AP load calculation method acknowledging the interference between STAs and APs is presented. Our simulations demonstrate that the proposed algorithm can improve the overall system throughput performance more than 50% and offers a better load distribution across the network compared to conventional association algorithm.

A novel transmit power control (TPC) bit estimation technique for FDD-UMTS downlink is proposed. Conventional FDD-UMTS downlink TPC bit estimation algorithm is based on coherent detection, which utilizes pilot bits for channel estimation and uses this estimate to remove the wireless channel effect on TPC bits. However, joint utilization of pilot and TPC bits can improve the detection performance as well as minimize the inherent overhead caused by excessive pilot bits usage in the transmission. In the proposed algorithm, pilot and TPC bits are used collectively for non-coherent detection of the power control command. Power increase and decrease orders are represented by two orthogonal vectors which are made up of pilot and TPC bits. TPC bit error rate (BER) performance comparisons of conventional and proposed algorithms are presented for various multi-path channels and slot formats. It is shown that in all the slot formats and different channel conditions, the proposed algorithm provides superior performances in terms of TPC bit error rate. This performance gain can go up to 15 dB at practical TPC BER (10-2) with certain channel conditions and slot formats.

High-speed downlink packet access (HSDPA) is an interface of UMTS systems for data communication. It combines 16-QAM modulation with low spreading factors to achieve high data rates. Generalized RAKE (G-RAKE) receiver is an advanced receiver, which can be employed in HSDPA to obtain reliable communication. In this work, we investigate iterative methods, which reduce overall complexity requirements of the G-RAKE receiver, without sacrificing its performance. The names of the methods are The Gauss-Seidel (GS), Successive Over-Relaxation (SOR), Conjugate Gradient (CG), and Preconditioned Conjugate Gradient (PCG). Our simulation results show that the PCG method provides the best trade-off between the complexity and required conditions.

Performance of wireless local area networks (WLANs) over fiber systems is investigated under multipath fading for different graded index fiber profiles and optical system imperfections. The effect of OFDM cyclic prefix to the multimode fiber dispersion is investigated for the first time. Comparison of the WLAN over fiber systems operating at 5 GHz and 60 GHz is presented. External modulators, namely Mach Zehnder external modulators, are employed in the system architecture. Wireless and optical impairments are attacked together and solved in a collaborative and efficient manner

The orthogonal matching pursuit (OMP) algorithm is an adaptive nonlinear algorithm for signal decomposition using an overcomplete dictionary. A tree-search based orthogonal matching pursuit (TB-OMP) has been proposed (Cotter et al. (2001)). Although the TB-OMP algorithm improves the approximation performance, its computation time requirement increases exponentially making the algorithm impractical for certain applications. In this paper, we propose the flexible tree-search based orthogonal matching pursuit (FTB-OMP). The algorithm provides design parameters that give flexibility to establish a tradeoff between approximation performance and experimental time complexity. Sparse signal representations are frequently required in problems related to signal processing and communication areas. The proposed FTB-OMP algorithm is a promising solution for such problems.

In this paper, we present a novel optical CDMA multi-user detector employing the orthogonal matching pursuit algorithm. The proposed system is compared with most of the receiver structures in the literature. It is shown by simulation results that the proposed detection architecture is a very promising candidate with its low computational complexity, and high detection performance. It is also shown to be more robust to low SNR and near-far effect when compared to most of the well-known optical CDMA receiver architectures.

In this paper, we apply adaptive algorithms in the SISO multiuser detector in order to avoid the need for a priori information. First, we present the optimum SISO parallel decision feedback detector for asynchronous DS-CDMA systems, which requires many system parameters. Then, we propose two adaptive versions of this SISO detector which are based on the normalized least mean square (NLMS) and recursive least squares (RLS) algorithms, respectively. The signature waveforms and relative delays of multiple users are unknown to the adaptive SISO detector. Only a training sequence is required for each user. Our SISO adaptive detectors effectively exploit the a priori information of coded symbols, which is based on soft inputs from a bank of single user decoders, to further improve their convergence performance. Furthermore, we consider how to select practical finite feedforward and feedback filter lengths to obtain good tradeoff between the performance and computational complexity of the receiver. Finally, Monte-Carlo simulation results are presented and compared.

In communications system design, it is frequently assumed that source symbols are equiprobable. However, in real life applications, this is not the case since most sources produce Gaussian samples. In this paper, we introduce a Karhunen Loeve transform (KLT) based integer to integer transform, I/sub 2/I KLT, over GF(q) that forces the symbols to uniform distribution. This transform can be used as an interface between sources with different distributions and communication systems designed according to uniform distributions.

The capacity of a multibeam satellite mobile communications system employing code division multiple access (CDMA) communications is presented. An important problem in applying the CDMA scheme is unequal received power levels at the receiver. In a CDMA system, capacity is maximized when all transmitted user signals are received at the minimum power necessary to attain the specified signal power to interference and noise power ratio (SINR). Due to inherent long propagation delay, power control techniques cannot perfectly compensate the power fluctuations in mobile satellite channels. Consequently, the capacity of the system is reduced relative to system with perfect power control (PPC). This paper examines the performance of a multibeam satellite CDMA system using imperfect power control. Statistical characteristics (e.g. probability distribution function and cumulative distribution function) of mobile user bit energy to total interference ratios are obtained as a function of power control error and used for capacity calculations. The system capacity is calculated with a given outage probability and power control error (PCE).

In this paper, error performance of a serially concatenated QPSK space-time system is investigated on quasi-static, block and rapid fading channels. We consider outer nonrecursive convolutional and inner recursive space-time trellis code case and iterative decoding based on the maximum a posteriori (MAP) algorithm. The performance is evaluated by means of computer simulations and it is observed that when the recursive versions of some of the previously known space-time trellis codes are used as the inner codes, the Euclidean distance criterion based spaced-time codes lead to better error performance for both quasi-static and rapid fading channels. We also investigate the effects of various system parameters on the performance. We obtain the error performance for the large number of transmit and/or receive antennas increases the error performance improves.

Our objective is to design efficient coded modulation techniques with multi-stage decoding (MSD) for Rayleigh fading channels. The well-known rate design rule is conventionally used for AWGN channels. We extend the application of the rate design rule for multi-level coding by considering MSD for Rayleigh fading channels with interleaving. We model the fading channel as a time invariant additive non-Gaussian noise channels by assuming that the perfect channel state information is available at the receiver. The equivalent channel capacity curves that can be used for the multi-level code design for Rayleigh channels, and a code design example are presented. We demonstrate that a very good coding gain can be achieved if code rates are selected correctly.

For coded multiuser systems, an iterative receiver consisting of a soft-input soft-output (SISO) multiuser detector and a bank of single-user (SISO) decoders can provide a system performance which approaches that of the single user system after many iterations. In this paper, we transform the traditional linear multiuser detectors, namely the decorrelator and MMSE detector, into SISO detectors which can cooperate with single-user decoders iteratively. The resulting system performance converges quickly, while the computational complexity is proportional to the number of users squared. Both performance analysis and simulation results are provided. Finally, the comparison between these two types of linear SISO detectors is presented.

More efficient transmission of coded speech over packet switching systems can be achieved by channel coding. The redundancy introduced by channel coding to recover lost or impaired packets results in an increased traffic and an increased queuing loss. Hence there is a critical tradeoff between channel coding rate and queuing loss. We show that the channel loss rate, the traffic level and congestion rate affect the optimum channel coding rate.

Transmission of G.729A coded speech over packet switching networks including forward error correction is considered. Three buffer management policies are applied: simple, random and privileged. The privileged policy plays an important role to achieve quasi-uniform packet loss among multiple users. Its effect on spreading the loss among various sources and in avoiding consecutive or closely timed losses for any source is described. In this paper, the subjective quality improvement by correctly adapting the loss pattern to the sensitivity of the G.729A algorithm is described.

We provide a new fuzzy relaxation trellis code-book search algorithm over noisy channels. The new algorithm solves the problems associated with the LBG algorithm, in the sense of delivering relatively lower distortion configurations using short training sequences. Furthermore, the new approach is significantly less sensitive to the initialization process. The algorithm minimizes a weighted distortion measure averaged over both the source and the channel statistics. The weights are soft distortion-related reliability information, which are delivered by a soft trellis vector quantization algorithm (STVQ). The concept of soft compression is introduced by Haddad and Yongacoglu (see Proceedings of GLOBECOM'99, Rio de Janeiro, Brazil, 1999) using the forward-backward symbol-MAP algorithm. The work introduced in this paper is an extension to the work established for the noiseless channel case discussed by Haddad and Yongacoglu (see IEEE ICASSP 2000, Istanbul, Turkey, p.1882-6, 2000). Testing is performed using a first order Gauss-Markov source over several trellis structures.

Increasing the transmission speed and/or the loop length in asymmetric digital subscriber lines (ADSL) is highly desirable. This can be achieved by employing sophisticated channel coding techniques. We investigate the potential usage of turbo codes in ADSL discrete multitone (DMT) systems to improve the system performance. Using turbo coding in ADSL DMT systems is shown to give a 6 dB coding gain at a bit error rate (BER) as low as 10/sup -6/. To lower the decoding complexity, Gray mapping of turbo coded QAM symbols is proposed and a standard binary decoder is employed at the receiver. To counter impulse noise, another major impairment in subscriber loop transmissions, using turbo codes together with proper interleaving and erasure decoding results in very good performance.

This paper introduces a new codebook search algorithm for trellis vector quantization systems (TVQ). The development of the new algorithm is based on the symbol-MAP channel decoding algorithm, which is modified for data compression to deliver soft distortion-related reliability information. Following a rate-distortion theoretic approach, the soft information is used to derive a codebook search algorithm that is capable of solving the problems associated with the LBG algorithm. The derived algorithm is fuzzy in the sense that it follows a soft association rule, however, it is deterministic in the descent towards the global minimum distortion point. Although the derivation is general, the algorithm is tested using gray-scale images, which provide a nonconvex square-error distortion surface. As shown in the simulation section, the new algorithm provides lower energy codebooks (/spl sim/0.8 dB gain), while being significantly less sensitive to initial codebooks using short training image sequences.

The ADSL standard is based on using hard decision decoding of Reed-Solomon (RS) codes. The standard states that as an option a four dimensional 16-state trellis code can be concatenated with an RS code. The resulting structure is rather complex mainly because of the associated complexity of the Viterbi decoder of the trellis code. An alternative to this complex structure is to improve the performance when only RS codes are used. We propose to use a multilevel RS coding structure in ADSL systems based on discrete multitone (DMT) technique. The multilevel RS coding is shown to provide 1 to 2 dB additional coding gain improvements over conventional RS coding.

The design criterion of a joint source/channel soft decision decoder is developed with both binary convolutional codes and nonbinary dual-k codes. The performance of the modified decoder is evaluated and compared to the performance of the decoder proposed by Sayood et al. (1994) by Monte Carlo simulations. As expected, the soft decision system outperforms the hard decision system simulated by Sayood (1994). In the context of decoding 2 and 3-bit DPCM compressed images, we show the advantage of using the nonbinary dual-k code, which matches the alphabets of the source encoder output, over binary convolutional codes. Furthermore, simulation results verify that a coding gain is achieved by exploiting higher residual redundancy levels at the source encoder output.

This paper presents an efficient method for simulating the performance of multicarrier modulations. The method is based upon the Gauss quadrature rules and offers a significant computational advantage over commonly used Monte Carlo techniques. It takes into account the effects of intersymbol interference, interchannel interference and noise. BER performance curves of representative FFT based multicarrier systems for ADSL and VDSL are obtained using the simulation method described.

This paper studies the design and performance analysis of a noncoherent multiple tone-frequency shift keying (MT-FSK) modulation based balanced incomplete block design (BIB-design) from combinatorial theory. The performance analysis of MT-FSK signals in Rayleigh fading channels with diversity and diversity combining is studied. A noncoherent diversity receiver and combiner is introduced and a union bound expression for the bit error rate is obtained. The results show that MT-FSK with diversity create a multiplicative diversity and therefore performs better than the conventional MFSK system in terms of power and bandwidth efficiency with less complexity.

This paper studies the performance of frequency hopped/coherent M-ary PSK signals in the presence of partial-band multitone jamming. The probability density function for the jammed received signal phase is found and utilized in obtaining a probability of error expression. The analytical expressions to assess the performance under worst case multitone jamming are provided.

This paper presents an analytical evaluation of a direct-sequence/frequency-hopped code division multiple access (DS/FH-CDMA) system employing non-coherent multiple tone frequency shift keying (MT-FSK) modulation in a Rayleigh fading environment. Multiple-tones per symbol rather than single tone per symbol (as in conventional MFSK) is used to provide diversity in a frequency selective channel. In the performance evaluations, multiple access interference (MAI) has been taken into account and the capacity for uncoded as well as convolutionally coded systems have been calculated.

The performance of trellis coded-8PSK in the presence of cochannel interference is analyzed and compared with the performance of uncoded QPSK. The analytical expressions are derived and supported by simulating the bit error rate performance of different TC-8PSK systems. The analytical and simulation results show that TC-8PSK is slightly more robust to cochannel interference than uncoded QPSK.>

Differential detector structures that use decision feedback to partially remove the effect of destructive intersymbol interference from minimum-shift keying (MSK) are introduced. In comparison to the conventional two-bit differential detection of GMSK (Gaussian MSK), the proposed structures provide about 4-dB E/sub b//N/sub 0/ improvement when the premodulation filter time-bandwidth product is 0.25. As the premodulation filter becomes narrower, the advantages of the proposed receivers are more pronounced. Thus the bit-error-rate performance of differential detection is brought closer to coherent detection while avoiding the problems associated with the carrier recovery.>

An efficient modem is introduced for system applications which favor differential detection techniques. In differentially detected controlled transition PSK (DCTPSK), pulse-shaping techniques are used to achieve bandwidth and power efficiency in nonlinear channels. The baseband waveshapes, eye diagrams, and signal space diagram of DCTPSK are given; its bit error rate performance is calculated and its power spectral density is obtained. In a multicarrier adjacent channel interference environment, the compact spectrum of DCTPSK enables it to utilize the available bandwidth and power more efficiently than some well-known modulation techniques such as DQPSK and DMSK.